What is A Diode: The Ultimate Guide

Contents hide

A diode is simply an electronic piece featuring two terminals that favor one-way current flow while obstructing the opposite flow. This piece is often made from semiconducting materials like germanium.

The underlying article delves deep into the world of diodes, exploring their features, working principles, variations, and applications.

Diode Symbol

The standard diode symbol is represented by a straight line with a triangle in the middle. At both ends, there are positive and negative symbols. The triangle’s arrowhead indicates the flow of current from the anode to the cathode. The line on the triangle’s backside represents the cathode.

Diode Symbol
Diode Symbol

History of P-N Junction


The discovery of P-N junction diodes dates back to the 19th century when scrutiny into the electrical capabilities of distinct substances began.

In 1874, it was established that various materials such as galena conducted current in one direction only. This is known as the rectifying effect.

However, the discovery of the P-N junction diode was made in the mid-1930s by Russell Ohl. This diode features a positive semiconductor connected to a negative semiconductor hence the name P-N junction.

It is believed that Ohl made this discovery accidentally while looking into silicon rectifiers.

In the early years following the discovery of the P-N junction, germanium was the primary construction material. However, in the 1950s, germanium was substituted by silicon. Today, P-N junction diodes are the most heavily utilized rectifiers in electrical appliances.

Function of Diode

Owing to their exceptional electrical properties, diodes are commonly utilized in contemporary electronics. They are versatile, hence they are often utilized to serve multiple purposes. Here are the primary functions of contemporary diodes:

· Rectification

The primary function of diodes is rectification. These valuable components permit one directional current flow by obstructing reverse current flow. As such, they are often utilized to generate DC from AC. This is particularly useful in battery chargers used to power electrical devices that necessitate DC.


· Voltage Regulation

Certain diodes such as the Zener diodes are uniquely engineered to retain a constant voltage on both terminals. This explains their extensive deployment in voltage regulation circuits, which provide stable power to electronics irrespective of input variations.

Zener Diode Symbol
Zener Diode Symbol

· Signal Clipping

When a diode is laid parallel to a specific source of signal the signal amplitude can be restricted accordingly. This is because the diode will only conduct current after a specific voltage threshold is met. For this reason, diodes are commonly employed to achieve signal clipping.

· Signal Demodulation

Diodes are also quite helpful in communication systems. They are often deployed in amplitude modulation radio to retrieve the maiden audio signal from the carrier waves. They also facilitate audio duplication by remedying the amplitude modulation signal.

· Switching

Active forward-biased diodes facilitate current flow and this turns on the switch. Conversely, inactive reverse-biased diodes switch off the circuit. This enables the utilization of diodes as electronic switches.

Key Diodes Characteristics


Virtually all electrical appliances in our homes or workplaces rely on diodes for various functions like signal clipping, voltage regulation, and rectification. Underneath, we unearth the key features of diodes and their applicability to various electrical devices.

· Diode Terminals

Primarily, diodes are characterized by the presence of two terminals. This permits the one-dimensional flow of currents and the blocking of opposing currents. This is the primary characteristic of diodes, which permits their application in multiple industries.

· Forward Voltage Drop

The majority of diodes in use today are made from silicon and germanium. Silicon diodes typically have a voltage of 0.7 volts while germanium diodes have a voltage of approximately 0.3 volts. Voltage drop is an essential feature of diodes since it directly determines the amount of voltage needed for a diode to become active.

· Reverse Leakage Current

Whenever a diode is in the reverse bias condition, the flow of current in the diode tends to be converse. This brings about a reverse leakage current. However, this leakage current depends on the make of the diode.

· Maximum Reverse Voltage

The maximum reverse voltage of diodes is also known as the peak inverse voltage. Whenever a diode surpasses this voltage level, it becomes inactive or damaged, and an opposite current flow is initiated. For every diode, the manufacturer lays down specific maximum reverse voltage rates.

· Power Dissipation

For diodes, the decrease in voltage across the diode and the forward current flow determine the power dissipation of diodes. Diodes typically squander power as heat and this often happens when the diodes are in the forward-biased condition.

· Recovery Time

Diodes are components that are often used to switch on and off electrical devices. The recovery time of a diode captures the time a diode takes to shift from an active to a non-active situation. This characteristic of diodes allows their application in high-frequency applications, which often demand lesser recovery times.

· Frequency Limitations

Signal disruption and distortion are synonymous with diodes whenever they are utilized in high-frequency circuits. This is because diodes often exhibit inductance and captaincies. These effects ultimately impact the functioning of diodes in high-frequency circuits.

· Diode Packages and Physical Dimensions

Owing to the distinct demands of various applications, diodes are typically manufactured in distinct dimensions and packages. The distinction in size and dimension is primarily designed to influence the thermal properties of the diode as well as the circuit layout. Some of the prominently utilized diode packages include surface-mounted and through-hole packages.

· Depletion Zone in Diodes

Also referred to as the space charge region, the depletion zone is a region in the diode located across the diode’s intersection where the charge carriers are exhausted. Consequently, this leads to the obstruction of current flow in reverse-biased diodes.

Depletion Layer
Depletion Layer

· Anode and Cathode in Diodes

Diodes are characterized by two terminals, which are ideally distinguished by their positive or negative charge.

Typically, the anode is represented by the positive terminal, while the negative terminal is represented by the positive terminal. These terminal charges play a pivotal role in the orientation of the diodes.

P-N Diode Current-voltage Flow Characteristics

The vast majority of electronic appliances in use today rely on P-N diodes. However, the distinct circuits deployed in these devices utilize various types of P-N semiconducting diodes. Beneath, we examine the different types of P-N diodes and their respective current-voltage characteristics.

· P-N Diode

For a P-N junction diode to materialize, two distinct semiconductors must be interlinked. These conductors are either negatively or positively doped. This interlinking results in a junction with inimitable electrical attributes.

P-N Junction Diode
P-N Junction Diode

· Forward-Biased State

Diodes often experience two conditions, forward-biased and reverse-biased conditions. In the forward-biased state, diodes experience a shift in electrons from the negatively charged side toward the positively charged side. This consequently brings about an elevation in forward current and voltage.

Forward Bias
Forward Bias

· Reverse-Biased State

For reverse-biased diodes, the positive terminal is essentially linked to the negative terminal and vice-versa. This state mitigates the crossing of charge carriers and this is typically initiated by the respective electric field. The microampere ranges in conventional diodes remain constant whilst the reverse current hikes when the voltage range increases.

Reverse Bias
Reverse Bias

· Levelling Off

In forward-biased diodes, leveling off is experienced whenever the diode reaches its optimal saturation point. In this state, the diode has conducted as much current as it can within the given voltage.

Materials used to Manufacture Diodes

In the early days of diodes, one semiconducting material was primarily used to manufacture diodes.

However, over the years, technological advancements have made it possible to utilize different types of materials. Beneath we look at the most commonly utilized materials when it comes to diode construction.

· Germanium

Germanium is without a doubt one of the pioneering materials exploited to manufacture diodes. This substance is in use up to date because of its unique electrical properties. Diodes made using this material often exhibit a comparatively lower voltage drop, which qualifies their application in low-power applications.

· Silicon

Silicon began replacing germanium as the primary diode manufacturing material in the 1950s. Today, it is the most prominent diode manufacturing resource and this is mainly because of its exceptional electrical features.

Silicon is also plentifully available hence it is used to manufacture some of the most prominent diodes such as P-N junction and Schottky diodes.

· Silicon Carbide

Silicon carbide is revered for its exceptional thermal features as well as its ability to conduct electricity. This thermal resilience makes silicon carbide a perfect material for manufacturing diodes meant to be deployed in power electronics. Silicon carbide diodes can tolerate extreme temperatures and they demonstrate low reverse leakage current.

· Gallium Arsenide

Gallium arsenide is principally utilized to manufacture diodes for use in high-frequency applications like optical communication devices. This is because gallium arsenide diodes perform better than other diodes, even silicon diodes in high-speed applications.

· Gallium Nitride

In recent years, the prominence of gallium nitride as a diode manufacturing component has grown exponentially. This growth has been driven by the impressive breakdown voltage of the material as well as its faster switching speeds. Gallium nitride is mainly used to produce high-power diodes.

· Organic Materials

Organic diodes are manufactured from organic materials and they are primarily utilized in solar displays and cells. They are mainly compact and light in weight hence their widespread use in wearable electronic devices.

· Diamond

Diamond diodes are ideally manufactured from natural diamond fabric. Owing to the robust nature of diamonds, diamond diodes are quite durable and dependable. Their thermal conductivity is impeccable hence they are mainly utilized in tough conditions such as high temperatures.

P-N Junction Construction

P-N junction diodes draw their construction which sees the positively charged semi-conductors linked to negatively charged conductors at a specific intersection. Underneath, we look at the principal components of P-N junction diodes.

· Semi-Conducting Material

At the heart of P-N junction diodes lies a semiconductor material. There are numerous materials that have been exploited to manufacture high-performance diodes including silicon and germanium. These semi-conducting materials allow diodes to conduct current hence the employment of diodes in rectification and signal clipping applications.

· Positive and Negative Semi-Conductors

P-N junction diodes are composed of two terminals; the positive and negative semi-conductor types.

The P-type semiconductor mobile carriers are positively charged while the N-type semiconductor mobile carriers feature negatively charged carriers. In P-type semiconductors, trivalent impurities, which accept electrons are injected, resulting in the creation of crystal lattice holes

In the N-type semi-conductors, pentavalent impurities, which inject excess electrons are injected, resulting in the creation of negatively charged semi-conductors.

· Depletion Zone

In the P-N junction, the electrons from the negatively charged negative semiconductor mingle with the holes from the positively charged semiconductor to form a depletion region. This region or zone is characterized by exhausted charge carriers.

· Contact Layers

Both the positive and negative terminals of the P-N junction are fitted with metallic contact surfaces to facilitate connection to external devices.

Parts of a Diode

Diodes, the electrical pieces made up of two terminals serve numerous purposes. Their effectiveness is founded on the primary components they are made of. Here is a brief breakdown of the main parts that make up an effective diode.

Parts of a Diode
Parts of a Diode

· Anode

The anode is the positively charged terminal of the diode. It is often represented by a positive symbol, which lies on the backside of the triangle. For current to flow into the diode, it relies on the anode.

· Cathode

The negatively charged terminal of the diode is known as the cathode and is often represented by a negative symbol. The cathode often features on the diode’s triangle arrowhead. Current flowing from the diode utilizes the cathode.

· P-N Junction

Diodes consist of negatively charged regions (the P-regions) and negatively charged regions (the N-regions), which link up at an intersection referred to as the P-N junction. This junction is responsible for the current flow in diodes.

· Core Semi-Conductor Material

Semi-conducting materials are the heartbeat of diodes. These materials equip diodes with the capability to conduct electricity. Some of the most prominently utilized materials in diode construction are germanium and silicon.

· Encapsulating Casing

Diodes are often fitted into electrical devices which can be subjected to varying degrees of physical pressure or harsh environmental conditions. To mitigate unprecedented damage, these diodes are often housed in secure casings known as encapsulating casings.

How Diodes Work


Diodes are indispensable components of the electrical appliances we use in our daily lives. To optimize their effectiveness, it is essential to understand their working principles.

Here is a step-by-step guide to how contemporary diodes function.

  • Diode Structure: Diodes conduct electricity because they are made using semiconductor materials. They are principally made of two terminals; the anode and the cathode.
  • Holes and Electrons: The positively charged semi-conductor in diodes features surplus charge carriers that are positively charged. These carriers are known as holes. Conversely, the negatively charged semi-conductor features surplus carriers with a negative charge known as electrons.
  • Forward Bias: Forward bias is achieved when the anode and cathode of a diode are linked to the positive and negative terminals of the voltage source respectively. This brings about current flow as the holes and electrons maneuver across the P-N junction.
  • Reverse Bias: A reverse bias is achieved when a negative voltage is exerted on the positive terminal and a positive voltage is exerted on the negative terminal. This makes the diode resistant to current flow due to an increase in the depletion region.
  • Depletion Zone Formation: Connecting the positive source of a voltage source to the cathode and the negative voltage source to the anode creates a difference. As a consequence, the holes in the positively charged side move towards the negative side while the electrons in the negative side migrate to the positive side. This results in a depletion region characterized by zero charge carriers.

Forward Forward-biased Diodes vs. Reverse-biased Diodes

Diodes have two principal operational states; forward-biased and reverse-biased states. Beneath, we dig deeper into the differences that distinguish these two elaborate operational states.

Feature Forward Biased Diodes Reverse Biased Diodes
Voltage Polarity Here, the cathode is linked to the negative voltage source while the anode is linked to the positive voltage source. Here, the cathode is linked to the positive voltage source while the anode is linked to the negative voltage source.
Current Flow In forward-biased diodes, the current emanates from the anode and flows to the cathode. In reverse-biased diodes, the flow of current from the anode to the cathode is extremely rare or non-existent.
Voltage Drop These diodes experience a relatively higher voltage drop. For instance, silicon diodes have a voltage drop of around 0.7 volts. These diodes experience a relatively lower voltage drop (millivolts).
Diode Conductance These diodes are essentially active meaning they can facilitate the passage of current (active state). These diodes are essentially inactive meaning they are non-conductive. The current flow is ideally obstructed.
Applications They are highly versatile hence they are prominently employed in signal clipping, rectification, and switches among others. They are quite limited and their applications are mainly centered on protection against reverse voltage.


Types of Diodes

Electrical appliances utilize diodes for various purposes including rectification and signal capping. As such, manufacturers have come up with distinct diode types designed to serve different functions. Here are the most commonly utilized diodes:

· Laser Diodes

Also referred to as semi-conductor lasers, laser diodes primarily emit monochromatic light. This highly focused light is needed in electrical appliances such as barcode readers, laser pointers, and optical devices among others.

Laser Diode
Laser Diode

· Light Emitting Diodes

Light-emitting diodes, commonly known as LEDs, are specialized diodes characterized by light emission. This is often a consequence of electrical current passing through the diodes. They are typically manufactured in a range of distinct colors, making them ideal for signage and indicator lights.

Light Emitting Diode
Light Emitting Diode

· Zener Diodes

Zener diodes are different from most diode types given that their voltage remains uniform across both terminals. Their operation state is primarily reverse-biased hence their widespread utilization in voltage regulators. The constant voltage is achieved whenever a certain voltage threshold is met (Zener voltage).

Zener Diode
Zener Diode

· Schottky Diodes

Schottky diodes are characterized by a metal-coated junction made of semiconducting material. This gives them a high switching speed hence they are often utilized as electrical switches. Additionally, they have a low forward voltage drop, which makes them perfect for rectification and circuit clamping.

Schottky Diode
Schottky Diode

· Varactor Diodes

Varactor diodes are known for changing capacitance. Their capacitance fluctuates depending on the voltage applied.  This makes them suitable for electrical devices that require voltage-controlled capacitance like microwave frequency circuits.

Varactor Diode
Varactor Diode

· Avalanche Diodes

These diodes experience the avalanche effect hence the name avalanche diodes. Owing to this effect, avalanche diodes experience high-speed charge carrier augmentation whenever the diode’s voltage passes a set threshold. This makes them ideal for applications like microwave detectors and voltage clamping.

Avalanche Diode
Avalanche Diode

· Photodiodes

Photodiodes are unique diodes known for generating electrical energy from light. They have exceptionally high response times hence they are prominently used in optical communication systems. They are also highly sensitive to light, making them the best option for photovoltaic cells.


· Tunnel Diodes

These distinct diodes are known for their quantum mechanical tunneling, which gives them a negative resistance zone in their voltage-current curve.

Over the years, they have been primarily utilized in oscillators and amplifiers. However, in recent years, their usage has narrowed tremendously due to the invention of more efficient and effective diodes.

Tunnel Diode
Tunnel Diode

· Pin Diodes

Pin diodes consist of an intrinsic region in addition to the positive and negative regions featured in other diode types. The intrinsic zone typically exhibits low carrier levels allowing the diode to operate as a variable resistor. This qualifies the deployment of pin diodes in various high-frequency electronics.

Pin Diode
Pin Diode

P-N Junction Diode Applications

With technology constantly advancing, most of today’s tasks are accomplished with the aid of electronic devices. These electronics require current regulation and this is often achieved with the help of diodes. Underneath, we unravel the numerous applications that depend on contemporary P-N junction diodes.

· Rectification

The vast majority of electronic devices currently in use require DC current to function. However, most power supplies supply AC current thereby necessitating the need for an inverter. Diodes transform the AC current into direct current making them highly valuable for electronics requiring unidirectional energy flow.

· Voltage Regulation

Certain electronics necessitate a constant voltage to operate optimally and avert unprecedented damage. For these devices, zener diodes play a pivotal role. These diodes help regulate voltage output by ensuring the voltage remains constant despite fluctuations in the power source.

· Reverse Voltage Protection

Voltage polarity can cause electronic breakdown hence it is important to regulate reverse voltage. Typical P-N junction diodes help avert reverse voltage by preventing wrong current flow. This keeps electronic appliances safe from reverse polarity.

· Over Voltage Protection

Excessive spikes in voltage often damage electrical components. To avert costly electronics damage, most electronic devices are endowed with P-N junction diodes. These diodes ensure that the voltage levels in specific circuits do not exceed the recommended levels.

· Clipping Circuits

Clipping circuits is another prominent use of P-N junction diodes. Here, the diodes are principally employed to regulate signal amplitude. They achieve this by becoming active or conducting whenever a specific signal threshold is reached.

· Signal Demodulation

Diodes are commonly deployed in diode detectors and communication systems to demodulate signals. They play a significant role in audio retrieval and multiplication. They also aid in the reception of AM radio broadcasts.

· Light Emission

There are specific diodes designed for applications that necessitate light emission. These applications include indicator lights and various lighting appliances used in homes. Light emission is achieved in the forward-bias state.

· Power Conversion

To effectively supply power to electrical components that operate on DC current, P-N junction diodes play a significant role. They convert AC current to DC current while also regulating the voltage levels to mitigate damages.

· Logic Gates

Logic gates are the foundation blocks of contemporary circuits. Some of the common logic gates include AND and OR logic gates and they all feature P-N junction diodes.

· LED Screens

Diodes play an integral role in manufacturing LED screens and displays. In fact, most display screens available today are made from LED.


Does a Diode Have Polarity?

Yes. The polarity of diodes is demonstrated by their ability to conduct or not conduct. In forward-biased states, current flows through the diode, while in reverse-biased states, current does not flow through the diode.

How Long Do Diodes Last?

Diodes are generally long-lasting components with their average lifespan ranging from 25,000 to 50,000 hours of typical usage. However, this is dependent on multiple factors including:

  • Construction material quality
  • Level of usage
  • Operating conditions

Are Diodes Affected by Temperature?

Yes. The functionality of diodes can be tremendously impacted by temperature and other environmental conditions. Unfavorable temperatures can disrupt various electrical properties of diodes including forward voltage drop and reverse leakage current. It is therefore important to employ diodes in their favorable temperature conditions and adhere to the temperature ratings recommended by their designers.

How Can One Check If a Diode is Working Properly?

Diodes can malfunction or exhibit low-performance levels due to various reasons. It is therefore essential to check if a diode is working at its optimal best. To determine the condition of a diode, one can utilize numerous techniques and tools.  Here are some of the ways you can use to test a diode:

  • Physically examine the diode.
  • Use a multimeter to test the diode to measure the forward voltage drop.
  • Use an oscillator to determine the diode voltage waveform.


As you can see, diodes is one of the best inventions that has revolutionized the electrical and electronics industry. From switches, to display screens, all your need is the right type of diode.

Scroll to Top